The following excerpt is taken from What Every Christian Should Know About Satan. Order your copy in print, Kindle, or Audible versions here.

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In this post and others to follow, we’re going to consider several New Testament passages that depict Satan as the evil one.

Matthew 5:37 

“But let your ‘yes’ mean ‘yes,’ and your ‘no’ mean ‘no.’ Anything more than this is from the evil one.”

In this part of the Sermon on the Mount, Jesus addresses the issue of oath-taking, which plays a significant role in first-century Judaism. Jesus begins with an Old Testament reference: “Again, you have heard that it was said to our ancestors, You must not break your oath, but you must keep your oaths to the Lord” (Matt. 5:33; cf. Lev. 19:12; Num. 30:2; Deut. 23:21-23).

Then, Jesus follows with: “But I tell you, don’t take an oath at all: either by heaven, because it is God’s throne; or by the earth, because it is his footstool; or by Jerusalem, because it is the city of the great King. Do not swear by your head, because you cannot make a single hair white or black” (Matt. 5:34-36). 

Jesus does not forbid the taking of an oath in a court of law or a similar setting. In fact, he offers a response when the high priest puts him under oath (Matt. 26:63-64). But taking oaths has become so commonplace in Jesus’ day as to become meaningless. People have come to think that a lie between two individuals doesn’t concern God unless they invoke the divine name. In this case, they risk perjury for false statements, not to mention undermining God’s dignity.

Jesus’ command not to take an oath, then, is meant to tell his followers, in the strongest terms, that those who follow him must speak the truth. One must never take the approach that he or she is only telling the truth when they make an oath – a solemn statement affirmed to be true before God. 

Leon Morris explains: 

The Jews held that unless the name of God was specifically mentioned the oath was not binding; there were lengthy discussions about when an oath is or is not binding, and people would sometimes swear by heaven or earth or a similar oath and later claim that they were not bound by that oath because God was not mentioned. Jesus rejects such casuistry [an elaborate hierarchy of laws]. People should not swear oaths at all, certainly not by heaven, for that is the throne of God; to substitute heaven for God does not in fact avoid a reference to the deity, for heaven is his throne.

If heaven is God’s throne, then earth is his footstool (Isa. 66:1), so a person may not circumvent a direct reference to God by invoking earth. Nor should an oath be sworn by Jerusalem, God’s elect city (Lam. 2:1; Ps. 48:1-2). Many Israelites in Jesus’ day believed swearing by heaven, earth, Jerusalem, or one’s own head was less binding than swearing by God. But Jesus makes it clear that each of these belongs to God in its own way. Therefore, arbitrary distinctions are wrong.

Finally, Jesus says not to swear by our heads. To swear means to make a solemn declaration with an appeal to God, a divine being, or some sacred object in confirmation of what is said. To swear by the head means the swearer offers his head (that is, his life) if he is not speaking the truth. Jesus moves from the greatness of God to the smallness of people. We cannot change the color of even one hair on our heads (Matt. 5:36). So, why should we invoke God’s name – or our puny selves – to support our claims?

Followers of Jesus are not to split hairs to escape truthful conversations. No oath is necessary for the truthful person, and Jesus commands truthfulness from his followers. Jesus simply says to let our “yes” and “no” speak for themselves as reliable statements. James similarly writes, “Above all, my brothers and sisters, do not swear, either by heaven or by earth or with any other oath. But let your ‘yes’ mean ‘yes,’ and your ‘no’ mean ‘no,’ so that you won’t fall under judgment” (Jas. 5:12).

Jesus closes this section of his sermon by saying, “Anything more than this [a truthful yes or no] is from the evil one” (Matt. 5:37). Satan is the father of lies (John 8:44). His lies come in all shades: twisted truths, compromises, complete fabrications, and so on. But a half truth is a full lie. And any compromise with the truth results in a victory for the evil one. 

It doesn’t help to take an oath because that suggests we are only truthful when it really matters. Worse, it puts the reputation of God on the line. Since we are fallen creatures, swearing by our heads doesn’t enhance the truth. We are known to fashion our own brand of truth – and then fully believe it. 

For those who carry the name of Jesus, the message is simple: we are to be truthful at all times. While oaths have their proper place – in a court of law, for example – our conversations should reflect the character of Christ, who is the truth (John 14:6). People should not find it necessary to demand that we invoke God’s name to verify the truthfulness of our statements. If they do, it could be that our words more accurately mirror those of the evil one than of our Lord.  

Craig Keener remarks, “All oaths implicitly call God to witness, because everything that exists was made by him. For Jesus, no aspect of life except sin is purely secular.”

Next: Matthew 6:13